Mutational Variation Analysis of Porin Gene in Multidrug-Resistant Clinical Isolates of .

The present study deals with the outer membrane OprD porin protein in 29 clinical bacterial isolates of multidrug-resistant . porin gene expression was investigated using real-time reverse transcription-PCR. Amplicons from and its transcriptional regulator gene were sequenced and analyzed for mutations. Hypothetical models of selected mutant OprD-porin proteins were predicted and refined by homology modeling approach. ampliconic sequences were also screened for restriction fragment length polymorphism (RFLP). The gene was found to be downregulated in 89.7% ( = 26) of the isolates in comparison to the transcript levels in the reference strain -PAO (MTCC-3541). Interestingly, all these isolates displayed the presence of a conspicuous 8-bp deletion (GGCCAGCC) at nucleotide position 235 of regulatory gene. Based on the mutational patterns observed in gene, the isolates were classified into categories designated as A, B1-2, C1-4, D1-6, E1-2, and F. Our hypothetical models revealed that mutations were predominantly confined to the extracellular loops emanating from the β-barrel porin protein. These protein models also enabled clear visualization of loss of substantial portions of the truncated polypeptide. Incidentally, since most of the amplicons of the clinical isolates were found to display distinct RFLP banding patterns, our results also provide a useful diagnostic tool for detection of porin mutants.